The present invention is directed to an apparatus for extracting contaminants from soil, soil liquids, and/or soil gases. The 2-PHASE.TM. extraction process uses a high vacuum to remove the contaminants from the ground. Specifically, the present invention includes an air flow control apparatus which can be used to maintain this high vacuum by continuously supplying the optimal entrainment air ratio.
The 2-PHASE.TM. (a trademark of the Xerox Corporation) extraction process provides a method and apparatus for removing chemicals and other undesirable substances from a contaminated area of the ground. Generally speaking, an extraction tube or the like is placed within the contaminated area and a vacuum is applied such that a combined liquid and vapor stream is drawn from the ground through the tube. The liquid and vapor are then separated, and each phase is treated to remove contaminants. Such processes are disclosed in U.S. Pat. No. 5,464,309 (Mancini 309), U.S. Pat. No. 5,441,365 (Duffney), U.S. Pat. No. 5,358,357 (Mancini 357), U.S. Pat. No. 5,197,541 (Hess 541), U.S. Pat. No. 5,172,764 (Hajali), and U.S. Pat. No. 5,050,676 (Hess 676), all assigned to Xerox Corporation, Stamford, Conn., the assignee of the present invention.
Contaminants can be found in subsurface soil and groundwater, in the liquid or vapor phase. They can exist as discrete substances, or they can be mixed with and/or dissolved in groundwater and soil vapors. Various types of contaminants can be found in groundwater and soil, including volatile organic compounds, semi-volatile materials, metal contaminants, and the like. Such contaminants can be found in the vadose zone (the unsaturated layer that lies between the surface of the earth and the water table), at the interface between the vadose zone and the water table, and in the saturated zone below the water table.
A variety of techniques have been used for removal of contaminants and remediation of affected media. One technique entails the excavation and off-site treatment of the soil. Another technique entails saturating the contaminated soil with water in situ, causing the contaminants to be leached slowly from the soil by the water. The contaminated water can then be removed.
The 2-PHASE.TM. extraction process is a very effective technique for removing volatile and water soluble chemicals from a contaminated area of the ground, but seasonal changes and other natural events which regularly alter the height of the water table can adversely affect its operation. For example, during spring months the amount of groundwater present in a given area will often increase due to snow melt or precipitation run off. Since a greater volume of contaminated effluent must be extracted from sub-surface soil, the ratio of entrainment air to groundwater must be manipulated manually or the anti-gravitational force being applied to the effluent stream will be too small lift it from the ground.
During the summer, groundwater levels typically decrease, resulting in an increase in the depth of the vadose zone. This means that the amount of contaminated groundwater in the area will decrease and the amount of soil gas present will increase. This additional soil gas results in greater air flow within the extraction well. The increase in the flow of air causes a loss of vacuum which makes well operation inefficient.
In any season, the bottom of the extraction well must be kept at or very near the liquid-vapor interface within the well in order to maintain the entrainment of suspended liquid within the extracted air stream. If the liquid-vapor interface drops below the bottom of the well, the amount of air being supplied to the well must again be adjusted if the vacuum condition is to be maintained. Once ground water levels rise, the air supply must again be adjusted to optimize the vacuum or the extraction well will again operate inefficiently.
Thus, entrainment air must be adjusted as the groundwater level fluctuates if optimal vacuum delivery to the well formation is to be maintained, and efficient operation of the extraction well is to continue. The vacuum within the well is currently maintained by supplying atmospheric air through an inlet as the level of groundwater increases. As the groundwater level drops, the air supply is cut-off. This method of operation requires a technician or other maintenance person to physically travel out to the well site, and inspect the hardware to see if the well is operating properly. If the liquid is no longer being entrained, the technician must manually supply compressed air to the well to restart it. The valve must then be manually adjusted vary the flow of ambient air once the well begins to operate. Because a failure will not be detected until a physical inspection of the hardware is performed, the well may be inoperable for extensive periods of time. It is desirable to provide a way to automatically direct and regulate the amount of air that is applied to the well and extraction tube, as seasonal and other changes to the groundwater level take place. The present invention provides such means, thereby eliminating the need for human intervention and the costs and inconvenience associated with it.
The following disclosures may be relevant to various aspects of the present invention:
U.S. Pat. No. 5,464,309 (issued Nov. 7, 1995 to Mancini et al.) discloses certain aspects of the 2-PHASE.TM. extraction process for removing volatile organic chemicals from a contaminated area of the ground. A borehole is placed in the contaminated area to a depth below the water table, and a plurality of concentric pipes are placed in the borehole. Gas and a vacuum are simultaneously applied to the pipe system such that contaminated vapors and liquid are drawn from the soil into the pipes. The vapors and liquids are transported to the surface together and separated into two components. Each stream is treated to remove the contaminants. An apparatus for carrying out the process is also disclosed.
U.S. Pat. No. 5,358,357 (issued Oct. 25, 1994 to Mancini et al.) discloses other aspects of the 2-PHASE.TM. extraction process and apparatus in which vacuum extraction is used to remove soil contaminants in both the saturated and vadose zones. The invention comprises providing a borehole in the contaminated area to a depth below the water table, placing a vacuum extraction pipe inside of a riser pipe and placing both pipes into the borehole to a depth below the water table. The vacuum extraction pipe has at least one gas inlet situated below the groundwater level. A gas is introduced into the riser pipe while a vacuum is being introduced into the extraction pipe. Gases and liquid are drawn from the soil into the perforated riser pipe and from the riser pipe into the vacuum extraction pipe. Two-phase flow within the vacuum extraction pipe is initiated when gas is introduced into the vacuum extraction pipe below the groundwater level. Both the vapors and the liquid are transported to the surface as a two-phase common stream. The vapor and liquid streams are then treated to remove contaminants.
U.S. Pat. No. 5,050,676 (issued Sep. 24, 1991 to Hess et al.) and U.S. Pat. No. 5,197,541 (issued Mar. 30, 1993 to Hess et al.) disclose still other aspects of the 2-PHASE.TM. extraction process and apparatus used to extract contaminants from the ground. The invention entails vacuum withdrawal of liquid and vapor phases as a common stream, separation of the liquid and vapor phases, and subsequent treatment of the separated liquid and vapors to produce clean effluents. Two phase extraction employs a single vacuum generating device to remove contaminants in both the liquid stream and soil gases through a single well casing.
U.S. Pat. No. 4,323,122 proposed that a vacuum be applied in a borehole at the level of the water table, and that contaminants which are floating on the water could be drawn off by vacuum applied to the liquid at or around that level. The invention comprises a conduit extending from the ground surface to a point just above the water table, a collection head fitted on the lower end of the conduit, a collection vessel connected to the upper end of the conduit, and an exhaust means for creating less than atmospheric pressure in the vessel. The collection head has a liquid impermeable end portion and a liquid permeable intermediate portion for permitting the passage of liquid. The process comprises providing an opening in the ground to a point beneath the surface of the water table, positioning the conduit with the collection head in place so that the liquid permeable wall of the collection head is just above the surface of the water table, connecting the conduit to the collection vessel intake, and exhausting air and other gaseous materials from the vessel to cause liquid to flow into the collection head through the conduit into the vessel.
Accordingly, although known apparatus and processes are suitable for their intended purposes, a need remains for processes and apparatus for removing contaminated liquids and gases from soil with increased efficiency. Further, there is a need for apparatus' for automatically adjusting the amount of air that is supplied to the vacuum extraction well, so as to maintain the appropriate vacuum conditions throughout its operation.
All of the references cited herein are incorporated by reference for their teachings.